U.S. patent application number 12/328942 was filed with the patent office on 2010-06-10 for mixed catalyst for nox reduction and methods of manufacture thereof.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Dan Hancu, Hrishikesh Keshavan, Benjamin Hale Winkler.
Application Number | 20100143227 12/328942 |
Document ID | / |
Family ID | 42231307 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100143227 |
Kind Code |
A1 |
Keshavan; Hrishikesh ; et
al. |
June 10, 2010 |
MIXED CATALYST FOR NOx REDUCTION AND METHODS OF MANUFACTURE
THEREOF
Abstract
Disclosed herein is a catalyst comprising a binder; and a
catalytic composition, the catalytic composition comprising a first
catalyst composition that comprises a zeolite; and a second
catalyst composition that comprises a catalytic metal disposed upon
a porous inorganic material, wherein the porous inorganic material
is a metal oxide, an inorganic oxide, an inorganic carbide, an
inorganic nitride, an inorganic hydroxide, an inorganic oxide
having a hydroxide coating, an inorganic carbonitride, an inorganic
oxynitride, an inorganic boride, an inorganic borocarbide, or a
combination comprising at least one of the foregoing inorganic
materials; wherein the catalyst is in the form of an extrudate or
foam.
Inventors: |
Keshavan; Hrishikesh;
(Clifton Park, NY) ; Winkler; Benjamin Hale;
(Albany, NY) ; Hancu; Dan; (Clifton Park,
NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
ONE RESEARCH CIRCLE, PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
42231307 |
Appl. No.: |
12/328942 |
Filed: |
December 5, 2008 |
Current U.S.
Class: |
423/239.2 ;
502/60; 502/62; 502/64; 502/74; 502/77; 502/78; 502/79 |
Current CPC
Class: |
B01D 2255/104 20130101;
B01J 23/74 20130101; B01J 37/32 20130101; B01J 35/1019 20130101;
B01J 37/0018 20130101; B01J 29/44 20130101; B01J 29/7415 20130101;
B01J 37/0215 20130101; B01D 2255/20715 20130101; B01J 23/50
20130101; B01J 23/48 20130101; B01J 37/0009 20130101; B01D 53/9418
20130101; B01J 23/38 20130101; B01J 2229/42 20130101; B01J 29/064
20130101; B01J 29/65 20130101; B01J 37/04 20130101; B01D 2258/012
20130101; B01J 29/22 20130101; B01J 35/0006 20130101; B01J 29/126
20130101; B01D 2255/50 20130101; B01J 35/04 20130101; B01J 29/67
20130101 |
Class at
Publication: |
423/239.2 ;
502/60; 502/79; 502/78; 502/77; 502/74; 502/64; 502/62 |
International
Class: |
B01J 29/06 20060101
B01J029/06; B01J 29/064 20060101 B01J029/064; B01D 53/56 20060101
B01D053/56; B01J 29/072 20060101 B01J029/072 |
Claims
1. A catalyst comprising: a binder; and a catalytic composition,
the catalytic composition comprising: a first catalyst composition
that comprises a zeolite; and a second catalyst composition that
comprises a catalytic metal disposed upon a porous inorganic
material, wherein the porous inorganic material is a metal oxide,
an inorganic oxide, an inorganic carbide, an inorganic nitride, an
inorganic hydroxide, an inorganic oxide having a hydroxide coating,
an inorganic carbonitride, an inorganic oxynitride, an inorganic
boride, an inorganic borocarbide, or a combination comprising at
least one of the foregoing inorganic materials; wherein the second
catalyst composition is present in an amount from 45 weight percent
up to 80 weight percent based upon the weight of the catalytic
composition; and wherein the catalyst comprising the binder and
catalytic composition is in the form of an extrudate or foam.
2. The catalyst of claim 1, wherein the zeolite is zeolite Y,
zeolite beta, ferrierite, mordenite, ZSM-5, or a combination
comprising at least one of the foregoing zeolites.
3. The catalyst of claim 1, wherein the zeolite comprises
ferrierite.
4. The catalyst of claim 3, wherein the ferrierite has silicon to
aluminum molar ratio of 20.
5. The catalytst of claim 3, wherein the ferrierite has a surface
area of about 200 to about 500 m2/gm.
6. The catalytst of claim 1, wherein the catalytic metal is silver,
gold, palladium, cobalt, nickel, iron, or a combination comprising
at least one of the foregoing metals.
7. The catalyst of claim 1, wherein the porous inorganic material
is silica, alumina, titania, zirconia, ceria, manganese oxide, zinc
oxide, iron oxide, calcium oxide, manganese dioxide, silicon
carbide, titanium carbide, tantalum carbide, tungsten carbide,
hafnium carbide, silicon nitrides, titanium nitride, lanthanum
boride, chromium borides, molybdenum borides, tungsten boride, or
combinations comprising at least one of the foregoing borides.
8. The catalyst of claim 1, comprising the first catalyst
composition in an amount of about 20 weight percent to about 80
weight percent, based upon the weight of the catalytic
composition.
9. The catalyst of claim 1, wherein the binder comprises boehmite,
saw dust, methylcellulose or sugar.
10. The catalyst of claim 1, wherein the catalyst is in the form of
an extrudate, and wherein the extrudate has a thickness in a range
from about 1.0 mm to about 12 mm.
11. A method of making a catalyst, comprising: combining a first
catalyst composition, a second catalyst composition, and a binder
to form an intermediate catalytic composition; the first catalyst
composition comprising a zeolite; the second catalyst composition
comprising a catalytic metal disposed upon a porous inorganic
material, wherein the porous inorganic material is a metal oxide,
an inorganic oxide, an inorganic carbide, an inorganic nitride, an
inorganic hydroxide, an inorganic oxide having a hydroxide coating,
an inorganic carbonitride, an inorganic oxynitride, an inorganic
boride, an inorganic borocarbide, or a combination comprising at
least one of the foregoing inorganic materials; and forming the
intermediate catalytic composition into a foam or extrudate.
12. The method of claim 11, wherein the intermediate catalytic
composition is formed into a foam, and the method further
comprises: adding a solvent to the intermediate catalytic
composition to form a slurry; immersing a foaming agent template in
the slurry; and calcining the foaming agent template.
13. The method of claim 12, wherein the foaming agent template is
calcined at a temperature in a range between about 200 degrees
Celsius and about 1100 degrees Celsius.
14. The method of claim 11, wherein the intermediate catalytic
composition is formed into a foam, and the foam is formed by gel
casting.
15. The method of claim 11, wherein the intermediate catalytic
composition is formed into an extrudate, and the method further
comprises: drying the extrudate; and calcining the extrudate.
16. The method of claim 15, wherein the extrudate is calcined at a
temperature in a range from about 400 degrees Celsius to about 800
degrees Celsius.
17. The method of claim 11, further comprising: milling the first
catalyst composition prior to forming the intermediate catalytic
composition.
18. The method of claim 11, further comprising: milling the second
catalyst composition prior to forming the intermediate catalytic
composition.
19. The method of claim 11, wherein the zeolite is zeolite Y,
zeolite beta, ferrierite, mordenite, ZSM-5, or a combination
comprising at least one of the foregoing zeolites.
20. The method of claim 11, wherein the catalytic metal is silver,
gold, palladium, cobalt, nickel, iron, or a combination comprising
at least one of the foregoing metals.
21. The method of claim 11, wherein the porous inorganic material
is silica, alumina, titania, zirconia, ceria, manganese oxide, zinc
oxide, iron oxide, calcium oxide, manganese dioxide, silicon
carbide, titanium carbide, tantalum carbide, tungsten carbide,
hafnium carbide, silicon nitrides, titanium nitride, lanthanum
boride, chromium borides, molybdenum borides, tungsten boride, or
combinations comprising at least one of the foregoing borides.
.
22. A method of reducing NOx comprising: exposing an exhaust gas
stream comprising NOx to a catalyst; the catalyst comprising a
binder and a catalytic composition, the catalytic composition
comprising: a first catalyst composition that comprises a zeolite;
and a second catalyst composition that comprises a catalytic metal
disposed upon a porous inorganic material, wherein the porous
inorganic material is a metal oxide, an inorganic oxide, an
inorganic carbide, an inorganic nitride, an inorganic hydroxide, an
inorganic oxide having a hydroxide coating, an inorganic
carbonitride, an inorganic oxynitride, an inorganic boride, an
inorganic borocarbide, or a combination comprising at least one of
the foregoing inorganic materials; the first catalyst composition
and the second catalyst composition being mixed together to form a
mixture; wherein the catalyst in the form of an extrudate or
foam.
23. The method of claim 22, wherein the zeolite is zeolite Y,
zeolite beta, ferrierite, mordenite, ZSM-5, or a combination
comprising at least one of the foregoing zeolites.
24. The method of claim 22, wherein the catalytic metal is silver,
gold, palladium, cobalt, nickel, iron, or a combination comprising
at least one of the foregoing metals.
25. The method of claim 22, wherein the porous inorganic material
is silica, alumina, titania, zirconia, ceria, manganese oxide, zinc
oxide, iron oxide, calcium oxide, manganese dioxide, silicon
carbide, titanium carbide, tantalum carbide, tungsten carbide,
hafnium carbide, silicon nitrides, titanium nitride, lanthanum
boride, chromium borides, molybdenum borides, tungsten boride, or
combinations comprising at least one of the foregoing borides.
Description
FIELD OF THE INVENTION
[0001] The invention includes embodiments that relate to a catalyst
composition. The invention also includes embodiments that relate to
a method of making and/or using the catalyst composition.
BACKGROUND OF THE INVENTION
[0002] Regulations continue to evolve regarding the reduction of
oxide gases of nitrogen (NOx) for diesel engines in trucks and
locomotives. NOx gases may be undesirable. A NOx reduction solution
may include treating diesel engine exhaust with a catalyst that can
reduce NOx to N.sub.2 and O.sub.2 using a reductant. This process
may be referred to as selective catalytic reduction or SCR.
[0003] In selective catalytic reduction (SCR), a reductant, such as
ammonia, is injected into the exhaust gas stream to react with NOx
in contact with a catalyst. When ammonia is used, the molecule
forms nitrogen and water. Three types of catalysts have been used
in these systems. The types include base metal systems, and zeolite
systems. Base metal catalysts operate in the intermediate
temperature range (310 degrees Celsius to 400 degrees Celsius), but
at high temperatures they may promote oxidation of SO.sub.2 to
SO.sub.3. These base metal catalysts may include vanadium pentoxide
and titanium dioxide. The zeolites may withstand temperatures up to
600 degrees Celsius and, when impregnated with a base metal, have a
wide range of operating temperatures.
[0004] Hydrocarbons may also be used in the selective catalytic
reduction of NOx emissions. NOx can be selectively reduced by a
variety of organic compounds (e.g. alkanes, olefins, alcohols) over
several catalysts under excess O.sub.2 conditions. The injection of
diesel or methanol has been explored in heavy-duty stationary
diesel engines to supplement the hydrocarbon in the exhaust stream.
However, the conversion efficiency may be reduced outside the
narrow temperature range of 300 degrees Celsius to 500 degrees
Celsius. In addition, there may be other undesirable
properties.
[0005] A selective catalytic reduction catalyst may include
catalytic metals disposed upon a porous substrate. However, these
catalysts often do not function properly when NOx reduction is
desired. In addition, catalyst preparation and deposition on a
substrate may be involved and complex. As a result, the structure
and/or efficacy of the catalyst may be compromised during
manufacture. It is therefore desirable to have catalysts that can
effect NOx reduction across a wide range of temperatures and
operating conditions. It is also desirable if the method and
apparatus can be implemented on existing engines and do not require
large inventories of chemicals. It is further desirable to have a
method of making such catalysts that does not require washcoating a
substrate, whereby the processing steps do not compromise the
catalyst activity.
BRIEF SUMMARY OF THE INVENTION
[0006] In accordance with one embodiment of the invention, there is
provided a catalyst comprising a binder; and a catalytic
composition, the catalytic composition comprising a first catalyst
composition that comprises a zeolite; and a second catalyst
composition that comprises a catalytic metal disposed upon a porous
inorganic material, wherein the porous inorganic material is a
metal oxide, an inorganic oxide, an inorganic carbide, an inorganic
nitride, an inorganic hydroxide, an inorganic oxide having a
hydroxide coating, an inorganic carbonitride, an inorganic
oxynitride, an inorganic boride, an inorganic borocarbide, or a
combination comprising at least one of the foregoing inorganic
materials; wherein the catalyst is in the form of an extrudate or
foam.
[0007] In accordance with another embodiment of the invention,
there is provided a method of making a catalyst, comprising
combining a first catalyst composition, a second catalyst
composition, and a binder to form an intermediate catalytic
composition; the first catalyst composition comprising a zeolite;
the second catalyst composition comprising a catalytic metal
disposed upon a porous inorganic material, wherein the porous
inorganic material is a metal oxide, an inorganic oxide, an
inorganic carbide, an inorganic nitride, an inorganic hydroxide, an
inorganic oxide having a hydroxide coating, an inorganic
carbonitride, an inorganic oxynitride, an inorganic boride, an
inorganic borocarbide, or a combination comprising at least one of
the foregoing inorganic materials; and forming the intermediate
catalytic composition into a foam or extrudate.
[0008] In accordance with another embodiment of the invention,
there is provided a method of reducing NOx comprising exposing an
exhaust gas stream comprising NOx to a catalyst; the catalyst
comprising a binder and a catalytic composition, the catalytic
composition comprising a first catalyst composition that comprises
a zeolite; and a second catalyst composition that comprises a
catalytic metal disposed upon a porous inorganic material, wherein
the porous inorganic material is a metal oxide, an inorganic oxide,
an inorganic carbide, an inorganic nitride, an inorganic hydroxide,
an inorganic oxide having a hydroxide coating, an inorganic
carbonitride, an inorganic oxynitride, an inorganic boride, an
inorganic borocarbide, or a combination comprising at least one of
the foregoing inorganic materials; wherein the catalyst in the form
of an extrudate or foam.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The invention includes embodiments that relate to a foam or
extrudate catalyst. The catalyst is effective for reducing NOx
present in emissions generated during combustion in furnaces,
ovens, and engines.
[0010] As used herein, without further qualifiers a "catalyst" is a
substance that can cause a change in the rate of a chemical
reaction without itself being consumed in the reaction. A "slurry"
is a mixture of a liquid and finely divided particles. A "powder"
is a substance including finely dispersed solid particles. As used
herein, the term "calcination" is a process in which a material is
heated to a temperature below its melting point to effect a thermal
decomposition or a phase transition other than melting. A "zeolite"
is a crystalline metal oxide material that comprises a micro-porous
structure.
[0011] In one embodiment, the catalyst comprises a binder, and a
catalytic composition including a first catalyst composition and a
second catalyst composition. The first catalyst composition and the
second catalyst composition are mixed together to form a mixture
that reduces NOx present in an emissions stream. The first catalyst
composition comprises a zeolite while the second catalyst
composition comprises a catalytic metal disposed upon a porous
inorganic material. The inorganic material may be a metal oxide, an
inorganic oxide, an inorganic carbide, an inorganic nitride, an
inorganic hydroxide, an inorganic oxide having a hydroxide coating,
an inorganic carbonitride, an inorganic oxynitride, an inorganic
boride, an inorganic borocarbide, or the like, or a combination
comprising at least one of the foregoing inorganic materials. When
the catalyst is employed to reduce NOx generated in emissions from
furnaces, ovens and engines, a variety of hydrocarbons can be
effectively used as a reductant. In one embodiment, diesel can be
used as a reductant. The catalyst can reduce NOx while using higher
hydrocarbons having from about 5 to about 9 carbon atoms as a
reductant. The catalyst advantageously functions well across all
temperature ranges, especially at temperatures of about 325 degrees
Celsius to about 400 degrees Celsius.
[0012] The first catalyst composition comprises a zeolite. The
zeolites may be naturally occurring or synthetic, and may be in the
form of a powder. Examples of suitable zeolites are zeolite Y,
zeolite beta, ferrierite, mordenite, zeolite ZSM-5, or a
combination comprising at least one of the foregoing zeolites.
Zeolite ZSM-5 is commercially available from Zeolyst International
(Valley Forge, Pa.). In one embodiment, the zeolite is a ferrierite
having a silicon to aluminum ratio of about 20.
[0013] Examples of commercially available zeolites that may be used
in the first catalyst composition are marketed under the following
trademarks: CBV100, CBV300, CBV400, CBV500, CBV600, CBV712, CBV720,
CBV760, CBV780, CBV901, CP814E, CP814C, CP811C-300, CP914, CP914C,
CBV2314, CBV3024E, CBV5524G, CBV8014, CBV28014, CBV10A, CBV21A,
CBV90A. The foregoing zeolites are available from Zeolyst
International, and may be used individually or in a combination
comprising two or more of the zeolites.
[0014] In one embodiment, the zeolite particles may have an average
particle size of less than about 50 micrometers. In one embodiment,
the zeolite particles have an average particle size of about 50
micrometers to about 400 micrometers. In one embodiment, the
zeolite particles have an average particle size of about 400
micrometers to about 800 micrometers. In another embodiment, the
zeolite particles have an average particle size of about 800
micrometers to about 1600 micrometers.
[0015] The zeolite particles may have a surface area of about 200
m.sup.2/gm to about 300 m.sup.2/gm. In one embodiment, the zeolite
particles may have a surface area of about 300 m.sup.2/gm to about
400 m.sup.2/gm. In another embodiment, the zeolite particles have a
surface area of about 400 m.sup.2/gm to about 500 m.sup.2/gm. In
yet another embodiment, the zeolite particles have a surface area
of about 500 m.sup.2/gm to about 600 m.sup.2/gm.
[0016] Prior to combining the first and second catalyst
compositions, the zeolite may be calcined to produce the H form of
the zeolite, which has been found to be advantageous. The H form of
the zeolite is the protonic form of the zeolite. Commercially
available zeolites are typically obtained in the NH.sub.4 form.
During calcination, NH.sub.3 is released to create the H form of
the zeolite. In one embodiment, the zeolite does not comprise any
metal ions. It is important that the zeolite remains in the H form
during preparation of the catalyst. For example, if Ag attaches to
the zeolite (e.g. Ag-CP914C), the catalytic mixture may not show
the desired catalytic activity.
[0017] The parameters used for calcination will depend on the type
of zeolite used. In one embodiment, the zeolite is calcined at a
temperature in a range from about 100 degrees Celsius to about 300
degrees Celsius. In one embodiment, the zeolite is calcined at a
temperature in a range from about 300 degrees Celsius to about 600
degrees Celsius. In another embodiment, the zeolite is calcined in
air at a temperature in a range from about 600 degrees Celsius to
about 900 degrees Celsius. In yet another embodiment, the zeolite
is calcined in N.sub.2 at 100 degrees Celsius for 1 hr, at 550
degrees Celsius for 1 hr, and then in air at 550 degrees Celsius
for 5 hrs. Alternatively, the zeolite can be calcined in air at 550
degrees Celsius for 4 hrs with a very slow ramp rate such as 1
degree Celsius per minute in a dry air feed. The zeolite can also
be calcined under vacuum at similar conditions so as to avoid
alteration of the cage structure.
[0018] Desirably, the first catalyst composition is present in an
amount of from about 20 weight percent to about 30 weight percent,
from about 30 weight percent to about 40 weight percent, from about
40 weight percent to about 50 weight percent, from about 50 weight
percent to about 60 weight percent, from about 60 weight percent to
about 70 weight percent, or from about 70 weight percent to about
80 weight percent, based upon the total weight of the catalytic
composition.
[0019] As noted above, the second catalyst composition comprises a
metal disposed upon a porous inorganic material. The porous
inorganic materials are metal oxides, inorganic oxides, inorganic
carbides, inorganic nitrides, inorganic hydroxides, inorganic
oxides having a hydroxide coating, inorganic carbonitrides,
inorganic oxynitrides, inorganic borides, inorganic borocarbides,
or a combination comprising at least one of the foregoing inorganic
materials.
[0020] Examples of suitable inorganic oxides include silica
(SiO.sub.2), alumina (Al.sub.2O.sub.3), titania (TiO.sub.2),
zirconia (ZrO.sub.2), ceria (CeO.sub.2), manganese oxide
(MnO.sub.2), zinc oxide (ZnO), iron oxides (e.g., FeO,
.beta.-Fe.sub.2O.sub.3, .gamma.-Fe.sub.2O.sub.3,
.epsilon.-Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, or the like), calcium
oxide (CaO), manganese dioxide (MnO.sub.2 and Mn.sub.3O.sub.4), or
combinations comprising at least one of the foregoing inorganic
oxides. Examples of inorganic carbides include silicon carbide
(SiC), titanium carbide (TiC), tantalum carbide (TaC), tungsten
carbide (WC), hafnium carbide (HfC), or the like, or a combination
comprising at least one of the foregoing carbides. Examples of
suitable nitrides include silicon nitrides (Si.sub.3N.sub.4),
titanium nitride (TiN), or the like, or a combination comprising at
least one of the foregoing. Examples of suitable borides are
lanthanum boride (LaB.sub.6), chromium borides (CrB and CrB.sub.2),
molybdenum borides (MoB.sub.2, Mo.sub.2B.sub.5 and MoB), tungsten
boride (W.sub.2B.sub.5), or the like, or combinations comprising at
least one of the foregoing borides. In one embodiment, the
inorganic substrate is alumina.
[0021] The porous inorganic material may have a surface area of
from about 100 m.sup.2/g to about 200 m.sup.2/gm, to about 200
m.sup.2/g to about 300 m.sup.2/gm, from about 300 m.sup.2/g to
about 400 m.sup.2/gm, from about 400 m.sup.2/g to about 500
m.sup.2/gm, from about 500 m.sup.2/g to about 600 m.sup.2/gm, from
about 600 m.sup.2/g to about 700 m.sup.2/gm, from about 700
m.sup.2/g to about 800 m.sup.2/gm, from about 800 m.sup.2/g to
about 1000 m.sup.2/gm, from about 1000 m.sup.2/g to about 1200
m.sup.2/gm, from about 1200 m.sup.2/g to about 1300 m.sup.2/gm,
from about 1300 m.sup.2/g to about 1400 m.sup.2/gm, from about 1400
m.sup.2/g to about 1500 m.sup.2/gm, from about 1500 m.sup.2/g to
about 1600 m.sup.2/gm, from about 1600 m.sup.2/g to about 1700
m.sup.2/gm, from about 1700 m.sup.2/g to about 1800 m.sup.2/gm, or
from about 1800 m.sup.2/g to about 2000 m.sup.2/gm. In an exemplary
embodiment, the porous inorganic material has a surface area in a
range of from about 200 m.sup.2/g to about 500 m.sup.2/g.
[0022] The porous inorganic material may be in the form of
particles. Both the porous inorganic material and the second
catalyst composition may in the form of a powder.
[0023] The porous inorganic material has an average particle size
of about 0.2 micrometers to about 5 micrometers. In one embodiment,
the porous inorganic material has an average particle size of about
5 micrometers to about 25 micrometers. In another embodiment, the
porous inorganic material has an average particle size of about 25
micrometers to about 50 micrometers. In another embodiment, the
porous inorganic material has an average particle size of about 50
micrometers to about 75 micrometers. In another embodiment, the
porous inorganic material has an average particle size of about 75
micrometers to about 100 micrometers. In an exemplary embodiment,
the porous inorganic material has an average particle size of about
40 micrometers.
[0024] The catalytic metal comprises alkali metals, alkaline earth
metals, transition metals and main group metals. Examples of
suitable catalytic metals are silver, platinum, gold, palladium,
iron, nickel, cobalt, gallium, indium, ruthenium, rhodium, osmium,
iridium, or the like, or a combination comprising at least two of
the foregoing metals. In one embodiment, the second catalytic metal
is silver. Other suitable catalytic materials may include one or
more other noble metals. Other suitable catalytic materials may
include one or more transitional metals. Other suitable catalytic
materials may include one or more metals in the lanthanide series
such as cerium and samarium.
[0025] The average catalytic metal particle size is about 0.1
nanometer to about 500 nanometers. The catalytic metal is present
in the second catalyst composition in an amount of about 0.025 mole
percent (mol %) to about 5 mol %. In one embodiment, the catalytic
metal is present in the second catalyst composition in an amount of
about 5 mol % to about 20 mol %. In another embodiment, the
catalytic metal is present in the second catalyst composition in an
amount of about 20 mol % to about 30 mol %. In one embodiment, the
catalytic metal is present in the second catalyst composition in an
amount of about 30 mol % to about 40 mol %. In yet another
embodiment, the amount of catalytic metal in the second catalyst
composition is about 40 mol % to about 50 mol %.
[0026] The first catalyst composition and the second catalyst
composition may each be in the form of a powder. Prior to combining
the first catalyst composition and the second catalyst composition,
the catalyst compositions may be milled or pulverized to reduce
their particle sizes to the desired ranges disclosed herein. In one
embodiment, the second catalyst composition may be formed by first
milling the porous inorganic material, and then adding the
catalytic metal to the porous inorganic material. Suitable methods
for milling the first and second catalyst compositions include ball
milling, ultrasonic milling, planetary milling, jet milling, or a
combination thereof. In one embodiment, the first and second
catalyst compositions are ball milled.
[0027] In one embodiment, a second catalyst composition powder is
formed in the following manner. The catalytic metal and the porous
inorganic material are combined with a solvent to form a second
catalyst slurry. Suitable solvents for forming the slurry include
water, alcohols such as short chain alcohols, polar protic solvents
and polar aprotic solvents. The second catalyst slurry is then
milled using any of the techniques described hereinabove. The
second catalyst slurry is then dried by spray drying,
freeze-drying, or super-critical drying, followed by calcination to
form the second catalyst composition powder.
[0028] The parameters used for calcination of the second catalyst
composition will depend on the type of catalytic metal and the
porous inorganic material used to form the composition. In one
embodiment, the second catalyst composition is calcined in air at a
temperature in a range from about 100 degrees Celsius to about 400
degrees Celsius. In another embodiment, the second catalyst
composition is calcined at a temperature in a range from about 400
degrees Celsius to about 800 degrees Celsius. In yet another
embodiment, the second catalyst composition is calcined in air at a
temperature in a range from about 800 degrees Celsius to about 1100
degrees Celsius.
[0029] The second catalyst composition is generally present in the
catalytic composition in an amount of about 20 weight percent to
about 40 weight percent, based upon the total weight of the
catalyst composition. In one embodiment, the second catalyst
composition is present in an amount of about 40 weight percent to
about 60 weight percent, based upon the total weight of the
catalytic composition. In another embodiment, the second catalyst
composition is present in an amount of about 60 weight percent to
about 80 weight percent, based upon the total weight of the
catalytic composition. In an exemplary embodiment, the second
catalyst composition is present in an amount of about 45 weight
percent to about 55 weight percent, based upon the total weight of
the catalytic composition.
[0030] Examples of suitable binders for use in the catalyst include
permanent binders and temporary binders. The binders may be organic
or inorganic binders. A permanent binder is added to the catalyst
and is not removed. An example of a permanent binder is boehmite.
Temporary binders are usually organic and are added to the catalyst
to aid in extrusion and forming foams. Temporary binders are
typically removed upon calcination of the catalyst. Examples of
temporary binders include saw dust, methylcellulose type binders
and sugar.
[0031] The binder is combined with the first catalyst composition
and the second catalyst composition to form an intermediate
catalyst composition. In one embodiment, the first catalyst
composition and the second catalyst composition are first combined
to form a catalytic composition. The binder is then added to the
catalytic composition to form the intermediate catalytic
composition.
[0032] In one embodiment, the intermediate catalytic composition is
formed into an extrudate using any method known to those skilled in
the art. In one embodiment an extrusion mull is prepared from the
catalytic composition. The extrusion mull is prepared by mixing the
components of the intermediate catalytic composition together until
a homogenous mull is formed. A high-speed planetary mixer may be
used to form the extrusion mull. The mull is then passed through an
extruder such as a BB Gun extruder, available from The Bonnot
Company, Uniontown, Ohio.
[0033] In one embodiment the extrudate has a thickness in a range
of from about 1.0 mm to about 4.0 mm. In one embodiment the
extrudate has a thickness in a range of from about 4.0 mm to about
7.0 mm. In another embodiment the extrudate has a thickness in a
range of from about 7.0 mm to about 9.0 mm. In yet another
embodiment, the extrudate has a thickness in a range of from about
9.0 mm to about 12 mm.
[0034] Following the extruding process, the extrudate is dried. The
extrudate may be dried at a temperature in a range of from about 25
degrees Celsius to about 40 degrees, from about 40 degrees Celsius
to about 80 degrees Celsius or from about 80 degrees Celsius to
about 110 degrees Celsius. In one embodiment, the extrudate is
dried in a box oven at a temperature of 80 degrees Celsius for
approximately 6 hours.
[0035] The extrudate is then calcined at a temperature in a range
of from about 400 degrees Celsius to about 500 degrees Celsius. In
another embodiment, the extrudate is calcined at a temperature in a
range from about 500 degrees Celsius to about 600 degrees Celsius.
In yet another embodiment, the extrudate is calcined at a
temperature in a range from about 600 degrees Celsius to about 800
degrees Celsius.
[0036] In an alternative embodiment, the intermediate catalytic
composition comprises a foaming agent, and the composition is
formed into a foam using any method known in the art. For example,
a foam may be produced by gel casting the intermediate catalytic
composition.
[0037] Any suitable foaming agent may be used in the intermediate
catalytic composition. For example, the foaming agent may be an
organic solvent that foams under heat or via a chemical reaction.
Suitable organic solvents include, but are not limited to
Hypol.RTM., a hydrophilic polyurethane prepolymer available from
Dow Chemical Company. Alternatively, the foaming agent may be a
template, such as a polyurethane foam or a cellulose foam.
[0038] If a foaming agent template is utilized, the intermediate
catalytic composition is formed into a slurry. The slurry comprises
the first catalyst composition, the second catalyst composition,
binder and a solvent. Suitable solvents for forming the catalytic
composition slurry include water, alcohols such as short chain
alcohols, polar protic solvents and polar aprotic solvents. The
foaming agent template is then immersed in the intermediate
catalytic slurry.
[0039] After immersing the foaming agent template into the slurry,
the template is calcined at a temperature between about 200 degrees
Celsius and about 500 degrees Celsius, from about 500 degrees
Celsius to about 800 degrees Celsius or from about 800 degrees
Celsius to about 1100 degrees Celsius. The coated foaming agent
template typically is first calcined to burn off the template. This
temperature is based on TGA-DTA analysis on the foaming agent
template. Typically the sample is isothermally soaked at a
temperature just below where the foaming agent starts to decompose
and held for an extended period of time until all the organic
foaming agent is removed. The calcination then proceeds further at
a higher temperature.
[0040] In one embodiment, the catalyst is disposed in the exhaust
stream of an internal combustion engine. The internal combustion
engine can be present in an automobile or in a locomotive. The
catalyst reduces NOx to nitrogen at rates that are superior to
conventional catalysts.
[0041] The following examples, which are meant to be exemplary, not
limiting, illustrate compositions and methods of making some of the
various embodiments of the catalysts described herein.
EXAMPLES
Example 1
Preparation of Second Catalyst Composition
[0042] .gamma.-Al.sub.2O.sub.3 can be obtained commercially from
various sources including UOP LLC, Des Plaines, Ill. AgNO.sub.3,
ethanol and high purity ZrO.sub.2 media are added to the
.gamma.-Al.sub.2O.sub.3 to form a second catalyst slurry as
indicated in Table 1. The second catalyst slurry is ball milled for
24 hours and dried at 80 degrees Celsius for 8 hours. The fine
powder is calcined in air slowly to 600 degrees Celsius to form
Ag--Al.sub.2O.sub.3.
TABLE-US-00001 TABLE 1 Slurry preparation for Ag--Al.sub.2O.sub.3
Alumina (g) AgNO.sub.3 (g) Ethanol (g) ZrO.sub.2 (g) Mill time (h)
50 2.435 50.00 100 24
Example 2
Preparation of Second Catalyst Composition
[0043] A second catalyst slurry is prepared by combining 30 g of
.gamma.-Al.sub.2O.sub.3, 70 g of water, and 250 g of high purity
ZrO.sub.2 media. HNO.sub.3 is added to the slurry to adjust the pH
of the slurry to between 3.5 and 4.5. The slurry is ball milled for
24 hours, and 2.3 g of AgNO.sub.3 is added to the slurry. The
second catalyst slurry is ball milled for an additional 30 minutes,
and then freeze dried in a Mill Rock freeze dryer under a pressure
of 300 mTorr. The freeze drying cycle is shown in Table 2
below.
TABLE-US-00002 TABLE 2 Freeze Drying Cycle Temp (.degree. C.) Time
(min) -55 240 -50 240 -45 240 -40 240 -35 240 -30 240 -25 240 -20
240 -15 240 -10 240 -5 240 0 240 5 240 10 240 15 240 20 240 25 240
30 240 35 240 40 240
Example 3
Preparation of First Catalyst Composition
[0044] Ferrierite zeolite CP914C obtained from Zeolyst
International, Valley Forge, Pa. was calcined in order to convert
the ferrierite to its H form. The ferrierite powder is calcined in
N.sub.2 at 110 degrees Celsius for 1 hr, at 550 degrees Celsius for
1 hr, and then in air at 550 degrees Celsius for 1 hr.
Example 4
Preparation of Catalyst Extrudate
[0045] The Ag--Al.sub.2O.sub.3 powder prepared in Example 1 and the
ferrierite zeolite powder prepared in Example 3 are combined in a
ratio of 4:1. The powders are mixed together with a high speed
planetary mixer. The powders are mixed in multiple cycles at 2000
rpm for 30 seconds, until a homogenous mull is formed.
[0046] The mull is extruded in a BB Gun extruder with an auger
speed of 5 rpm at 1000 psi to form extrudates having a thickness of
1/16 inch. The extrudates are dried in an oven at 80 degrees
Celsius for 4 hrs, and then calcined in dry air with a molecular
sieve oil filter to trap any organics in the air feed. The
extrudates are calcined at 600 degrees Celsius for 4 hrs.
Example 5
Preparation of Catalyst Foam
[0047] The Ag--Al.sub.2O.sub.3 powder prepared in Example 1 and the
ferrierite zeolite powder prepared in Example 3 are combined in a
ratio of 4:1. Water is added to the powder mixture to form a
slurry. A polyurethane foam is immersed in the slurry. The excess
slurry is removed from the foam by gently squeezing the foam. The
foam is dried at 100 degrees Celsius for 3 hours, and the foam is
then calcined as indicated in Table 3. The dwell time is the period
of time the foam is kept at a specific temperature, i.e. the
isothermal hold time.
TABLE-US-00003 TABLE 3 Calcination Cycle for Catalyst Foam
Atmosphere Ramp Rate Temp (.degree. C.) Dwell time (hr) Nitrogen 1
125 2 Nitrogen 1 250 10 Nitrogen 1 550 4 Air -- 550 5 Air 1 25
--
[0048] All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are combinable with each other. The terms
"first," "second," and the like as used herein do not denote any
order, quantity, or importance, but rather are used to distinguish
one element from another. The modifiers "about" and "approximately"
used in connection with a quantity are inclusive of the stated
value and have the meaning dictated by the context (e.g., includes
the degree of error associated with measurement of the particular
quantity). The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context.
[0049] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
* * * * *